I had a new requirement yesterday:

• Display only the top level menu items in the traditional DotNetNuke menu
• On lower-level pages, display a vertical menu in the left column with links to children of the current page.

If you remove pages from the NAV menu by unchecking the "Include in Menu?" checkbox, then the LINKS module doesn't show those pages either.  

This was our solution:

• Add ExpandDepth="1"  andPopulateNodesFromClient="False" as attributes of dnn:NAV in the skin file.  This displays only the to-level pages.
• Add Alignment="vertical"  and Level="Child" as attributes to dnn:LINKS.

For some pages, we will want to show pages at the same level on the vertical menu.  For this, we will create a second skin with Level="Same" for the LINKS skin object.